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\fB1. \fRYou have made some commits, but realize they were premature to be in the "master" branch. You want to continue polishing them in a topic branch, so create "topic/wip" branch off of the current HEAD.

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\fB2. \fRRewind the master branch to get rid of those three commits.

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\fB1. \fRYou are happily working on something, and find the changes in these files are in good order. You do not want to see them when you run "git diff", because you plan to work on other files and changes with these files are distracting.

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\fB2. \fRSomebody asks you to pull, and the changes sounds worthy of merging.

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\fB3. \fRHowever, you already dirtied the index (i.e. your index does not match the HEAD commit). But you know the pull you are going to make does not affect frotz.c nor filfre.c, so you revert the index changes for these two files. Your changes in working tree remain there.

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\fB4. \fRThen you can pull and merge, leaving frotz.c and filfre.c changes still in the working tree.

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\fB1. \fRTry to update from the upstream resulted in a lot of conflicts; you were not ready to spend a lot of time merging right now, so you decide to do that later.

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\fB2. \fR"pull" has not made merge commit, so "git reset --hard" which is a synonym for "git reset --hard HEAD" clears the mess from the index file and the working tree.

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\fB3. \fRMerge a topic branch into the current branch, which resulted in a fast forward.

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\fB4. \fRBut you decided that the topic branch is not ready for public consumption yet. "pull" or "merge" always leaves the original tip of the current branch in ORIG_HEAD, so resetting hard to it brings your index file and the working tree back to that state, and resets the tip of the branch to that commit.

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Interrupted workflow

Suppose you are interrupted by an urgent fix request while you are in the middle of a large change. The files in your working tree are not in any shape to be committed yet, but you need to get to the other branch for a quick bugfix.